INCOMPATIBLE KINEMATIC CONDITIONS

Altair Forum User

Hello Guys,

While running a simulation, I got warning 'INCOMPATIBLE KINEMATIC CONDITIONS IN MODEL.' I am analysing crash case. First, I created rigid and then I applied initial velocity on the rigid node. As my initial velocity is in the Z direction, so while creating rigid, I keep DOF 3( translation along the Z axis) of rigid unconstrained. So, why I am getting this warning? Is there another reason to get this warning?

Thank You for your help.

Altair Forum User

Hi Sanket,

Nodal constraints are based on kinematic conditions applied on nodal DOF. This is an undesired warning in a mode and need to find out where the nodes are over constrained or where the constraints are violating the loads applied. As a workaround, for rigid, constrain in all directions and apply initial velocity in all nodes including the master node of the rigid and try running the analysis.

 

Altair Forum User

Hello George,

Thanks for the reply. 

In my case, I have a 'plate' as a component and I created rigid on this plate ( rigid structure made up of all nodes of the plate). In my simulation result, I also want to know the deflection occurs in the plate after impact. But as u said, if I constrain all DOF of rigid, it won't allow deflecting my plate. And I won't get a result of deflection on a plate.

Therefore, I kept DOF 3 of rigid (the nodes, which are part of rigid) unconstrained, as my velocity is in Z-direction. What I thought, if I do the same, it allows my plate to deflect in the Z direction and I will get deflection result. Am I thinking right?

And you said, I should apply velocity on each node of rigid as well as a master rigid node. But I saw one video, in that he showed that, if I apply velocity on a master rigid node, it will automatically apply on every node, which is part of rigid. Is it wrong? Initial velocity( with the same magnitude) can not apply to each node by this way? Or is it distribute among all nodes like ' velocity on each load= (Velocity magnitude) / (no. of nodes)'

Please, help me to clarify my doubts.

Thanks Once again/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />

gopal_rathore

Hi,

When you create a rigid body, the body will not deform since it has become rigid and leads to no relative displacement between nodes, so no deformation values . But when we apply certain velocity or any other imposed motion, it can be displaced , provided it has free dof in that direction, Thus you will get displacement values of the body with time. as you have mentioned , the direction of motion is z and z-dof is free, I think this is fine. Check  0000.out file and see where the incompatible kinematic condition is being raised also once review the boundary conditions. 

 

Altair Forum User

Hi Sanket,

When you assign load in the independent node of the rigid body, it will applied to all slave nodes of the rigid body. But in some cases we will apply to all nodes including master node.

You can check the starter out file for more information on the incompatible kinematic condition and also you can check how much energy error is developing during the run.

Altair Forum User

Thank you, Gopal and George.

As far as I think, there is no conflict between boundary conditions and rigid body. As per you guys said, I checked starter out file but it shows like

 

''''''     WARNING ID :          446
** WARNING IN RIGID WALL
DESCRIPTION :  
   -- RIGID WALL ID : 2
   -- RIGID WALL TITLE : Rwall
   6904 NODES HAVE BEEN REMOVED FROM RWALL,
   DUE TO INCOMPATIBLE KINEMATIC CONDITIONS

WARNING ID :          312
** INCOMPATIBLE KINEMATIC CONDITIONS IN MODEL
DESCRIPTION :  
    864 INCOMPATIBLE KINEMATIC CONDITIONS IN MODEL
                                             
                                             
 SUMMARY OF POSSIBLE INCOMPATIBLE KINEMATIC CONDITIONS :
 -----------------------------------------------------
                                  
 - POSSIBLE INCOMPATIBLE KINEMATIC CONDITIONS BETWEEN:
     BOUNDARY CONDITION
     RIGID BODY   '''''''''''

 

And I applied velocity on each node include the master node of rigid, but it still shows the same warning. And when simulation comes to end error is around -0.1% to -0.5%.

 

 

Altair Forum User

Hi Sanket,

This warning seems to be related with the rigid wall. And it is not generating much energy in the model. And so, it seems like can be ignored.

This is a limitation of rigid walls , that is  Incompatible Kinematic Condition – a result of nodes belonging to another kinematic condition and the rigid wall.

In Help Menu, please search for Incompatible Kinematic Conditions and there these scenarios are explained.

Altair Forum User

Thank you, George...

Could you help me in optimisation in Radioss? I have gone through Altair help option, where it says 

 

 

define variables and responses:

1.	From the Menu Bar, select Process, then Study, then Optimization, then Edit Parameters.

 

 

But I am not getting an option of Process in Menu Bar  anywhere in Radioss GUI. I am using HW14 version. How and where I can get this option?

Altair Forum User

Hi Sanket,

Please provide the tutorial or example which you are referring. I think you are referring HyperStudy tutorial.

Altair Forum User

Hello George,

 

http://www.altairhyperworks.com/hwhelp/Altair/hw14.0/help/hc/hc.htm?hc_m-opt.htm  here I am reading some information about optimisation, but now I realised this information is for Hypercrash not for Radioss. But could u suggest me , how to start optimisation in Radioss? Where I can set constrain, design variable and responses?

Because I haven't seen optimisation option in Radioss and I read that optimisation is possible in Radioss 13 and 14 version.

http://www.altairhyperworks.com/hwhelp/Altair/hw14.0/help/hwsolvers/hwsolvers.htm?radioss_optimization_ug.htm I have gone through this, but still, confuse from where I will get ' <name.radopt>' file.

Thanks

 

Altair Forum User

Hi Sanket,

Optimisation in RADIOSS is not supported in HyperMesh now. but very soon it will be updated in the coming version.

Altair Forum User

Hello George,

So, is there any way to optimise my case? Or it is not possible?

Altair Forum User

Hi Sanket,

We have an example in Help Menu, Example 51 - Optimization in RADIOSS for B-Pillar (Thickness optimization). In that example, you can manually edit the parameters in the radopt file (in textpad) and can run the analysis. Another option is you can convert the file into OptiStruct and can continue the optimization in OptiStruct. Also I recommend you to review ESLM for Nonlinear Response Optimization in Help Menu for nonlinear response optimization.

Altair Forum User

Hi George,

Thanks for your help. I will follow the procedure recommended by you and If I get some problem then I will contact you back.

Thanks once again/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />.